Flame control in the buoyancy-dominated fluid dynamics region

ABSTRACT

A burner system includes a nozzle configured to emit a fuel stream for the support of a flame, and first and second electrodes, each configured to apply electrical energy to a flame supported by the nozzle. The first electrode is positioned in a momentum-dominated fluid dynamics region of the flame, while the second electrode is positioned in a buoyancy-dominated fluid dynamics region. Application of charges to the flame via the electrodes can be employed to control flame characteristics in the buoyancy-dominated fluid dynamics region, such as shape and position.

The present application claims priority benefit from U.S. Provisional Patent Application No. 61/773,740, entitled “FLAME CONTROL IN THE BUOYANCY-DOMINATED FLUID DYNAMICS REGION”, filed Mar. 6, 2013; which, to the extent not inconsistent with the disclosure herein, is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to combustion systems, and more particularly, to electrode arrangements that affect flame shape and position.

BACKGROUND

Combustion systems are employed in a vast number of applications, in industry and commerce, and in private homes.

SUMMARY

According to an embodiment, a method for controlling a characteristic of a flame in a burner system includes supporting a flame in a fuel stream and modifying a characteristic of the flame by application of electrical energy. The application of electrical energy includes applying a first electric charge to the flame at a first location that is upstream from a buoyancy-dominated flow region of the flame and applying a second electric charge to the flame at a second location that is downstream from a momentum-dominated flow region of the flame, such that the first and second electric charges interact.

According to another embodiment, a method for controlling a characteristic of a flame in a burner system includes supporting a flame in a fuel stream, identifying a flame holding region of the flame, a momentum-dominated flow region of the flame, and a buoyancy-dominated flow region of the flame, and modifying a characteristic of the flame by an application of electrical energy. The application of electrical energy includes applying a first electric charge to the flame at a first location that is upstream from the buoyancy-dominated flow region of the flame and applying a second electric charge to the flame at a second location that is downstream from the momentum-dominated flow region of the flame, such that the first and second electric charges interact.

According to another embodiment, a method for controlling a characteristic of a flame in a burner system includes, in a fuel stream, supporting a flame that is characterized by a momentum-dominated flow region and buoyancy-dominated flow region, each having dimensions sufficient for the application of electrical energy. A characteristic of the flame is modified by applying a first electric charge to the flame at a first location that is upstream from the buoyancy-dominated flow region of the flame and applying a second electric charge to the flame at a second location that is downstream from the momentum-dominated flow region of the flame, such that the first and second electric charges interact.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present disclosure are described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale.

FIGS. 1A and 1B show a burner system with regions of a flame identified to assist in the subsequent description of various embodiments.

FIGS. 2-6 each show a diagrammatic view of a burner system according to a respective embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, which are not to scale or to proportion, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings and claims, are not meant to be limiting. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of present disclosure.

In many of the embodiments disclosed below, various electrodes are described as being configured to apply a charge, an electrical potential, or electrical energy to a flame. While these terms are not synonymous, they are often used interchangeably, as there is significant overlap in their respective meanings, and it is often difficult to distinguish between them, or to do one without doing the others. For the purposes of the present disclosure and claims, they can be construed as being synonymous, except where a term is more explicitly defined.

Various burner systems are disclosed as embodiments. In practice, these and other embodiments are elements of more extensive combustion systems used in industry and commerce as parts of, for example, boilers, refineries, smelters, foundries, commercial and residential HVAC systems, etc.

FIGS. 1A and 1B are schematic diagrams of a portion of a burner 100 including a burner nozzle 102 configured to emit a fuel stream 104 along a longitudinal axis A of the nozzle and to support a flame 106, according to various embodiments. Particle velocity within the flame 106 is represented by arrows V. For the purposes of the present disclosure, a flame can be divided into three general regions or portions. The first region R₁, closest to the nozzle 102, is a flame-holding region. Adjacent to, and downstream from the flame holding region R₁ is the second region R₂, a momentum-dominated fluid dynamics region, and furthest downstream, the third region R₃ is a buoyancy-dominated fluid dynamics region.

The term flame particle refers primarily to gaseous atoms and/or molecules that comprise the fluid within a flame, as well as the small solid particles that may be entrained within the flame.

A flame front 108 of the flame is located in the flame holding region R₁. As fuel flows from the nozzle 102 in a downstream direction in the fuel stream 104 the flame front 108 is continually moving upstream. The velocity of the fuel stream 104 is a function of a number of factors, including the geometry of the nozzle 102 and the pressure of the fuel within the nozzle. Meanwhile, the flame propagation rate, i.e., the speed at which the flame front 108 moves upstream, depends upon the type of fuel, the amount of oxygen available, and the ambient temperature. When the flame propagation rate and the fuel stream velocity are equal, the flame 106 remains substantially stationary relative to the nozzle 102, and the flame is said to be stable. There are a number of structures and methods known in the art by which a stable flame can be obtained under many conditions and across a wide range of fuel stream velocities. According to the embodiments disclosed hereafter, the flame can be stabilized in accordance with any structure or method.

Within the momentum-dominated fluid dynamics region R₂ of the flame 106, the velocity and vector of flame particles within the flame 106 are substantially determined by the velocity and vector associated with the fuel stream 104. In this region, the velocity of the flame particles is sufficiently high that other factors have little influence on their vector. However, as the flame particles move downstream, they lose velocity, and the buoyancy of the flame 106, relative to the denser surrounding gases, tends to push the flame upward.

As the flame particles move further downstream and continue to lose velocity, the direction of movement is increasingly dominated by flame buoyancy. As shown in FIGS. 1A and 1B, within the regions R₁ and R₂, the position of the flame 106 relative to the longitudinal axis A of the nozzle 102 is substantially unchanged, regardless of the orientation of the nozzle. However, within the buoyancy-dominated fluid dynamics region R₃, which as characterized by a relatively low flame particle velocity, direction of movement of the flame 106 is dominated by buoyancy characteristics of the flame. Thus, for example, if the nozzle is oriented horizontally, as shown in FIG. 1B, the flame 106 will begin to move upward as it passes into the region R₃.

The shape of the flame 106, and the relative sizes of the three regions R₁-R₃, vary significantly, according to many factors. In some cases, the buoyancy-dominated fluid dynamics region R₃ is nonexistent, or very nearly so, as in, for example, some welding torch flames. In these types of flames, the fuel is substantially consumed before the velocity has dropped to a level where buoyancy can exert a significant influence. In other cases, the momentum-dominated fluid dynamics region R₂ is substantially nonexistent, as in the case of a candle flame or other flame in which little or no velocity is imposed on the fuel, so the flame velocity and vector are entirely controlled by other factors, including buoyancy.

As illustrated in the embodiments disclosed below, the inventors have recognized that application of electrical energy to the buoyancy-dominated fluid dynamics region R₃ of a flame can be most effective in controlling flame characteristics such as shape, position, height, breadth, etc. Turning now to FIG. 2, a burner system 200 is shown, according to an embodiment. In addition to the nozzle 102, the system 200 includes first and second electrode 202, 204, and a voltage source 206. The voltage source 206 is configured to apply an electrical potential to each of the first and second electrodes 202, 204. The voltage source 206 is preferably configured to independently and variably control the electrical potential applied to the electrodes. According to various embodiments, the voltage supply can be configured to apply positive or negative voltages of more than 10 Kv to the electrodes. According to some embodiments, the voltage supply is configured to apply an AC voltage, or an AC voltage with a DC offset.

The first electrode 202 is positioned adjacent to the flame 106 within the second region R₂ and configured to apply a first electric charge C₁ to the flame 106. For example, the first electrode 202 can be configured as an ion-emitting electrode, configured to introduce ions into the flame 106. Alternatively, the first electrode can be configured to apply an electrostatic charge to the flame 106, or to directly contact the flame and to apply a voltage potential to the flame, etc. Some different types of electrodes are shown and described with reference to various embodiments, but these are provided as examples, only. They do not represent all of the possible variations, nor are the embodiments limited to the specific electrode configurations shown or described. According to another embodiment, the voltage supply is electrically coupled to the nozzle 102, a portion of which functions as the first electrode. Where the term electrode is used in a claim, it is to be read on any structure that is capable of applying electrical energy to a flame, and is to be limited only by the express language of the claim.

The applied charge is shown in FIG. 2 as having a positive polarity, although the flame 106 can alternatively be charged to a negative polarity. The second electrode 204 is positioned adjacent to the flame 106 within the buoyancy-dominated fluid dynamics region R₃, and is configured to produce an electric field, or second electric charge C₂, adjacent to the flame in the third region R₃. Depending upon the desired effect, the electric field can have a same polarity as the first electrical charge C₁, or an opposite polarity. In the example of FIG. 2, the electric field has a negative polarity, which is opposite the positive polarity of the first charge C₁ applied by the first electrode 202. Accordingly, the second electrode 204 attracts the positively-charged flame 106 in a manner analogous to the way in which opposite poles of magnets are mutually attracted. The strength of the attraction of the second electrode 204 to the flame is a function of the magnitude of the charge applied to the flame 104, the voltage applied to the second electrode 204, and the distance between the second electrode and the flame.

In the embodiment of FIG. 2, the nozzle 102 is oriented horizontally. As explained with reference to FIGS. 1A and 1B, the trajectory or vector of the flame particles in the third region R₃ is normally dominated by the buoyancy of the flame. In the embodiment of FIG. 2, the electrical energy applied by the first and second electrodes 202, 204 is selected to generate an attraction sufficient to substantially offset the influence of buoyancy on flame particle vector, with the result that the flame 106 extends substantially along the horizontal axis A defined by the nozzle 102. It will be recognized that if the second electrode 204 is charged at the same polarity as the first electrical charge C₁, the second electrode 204 will repel the like-charged flame, producing an exaggerated upturn in the flame 106. Thus, by selection of the polarity and magnitude of the voltage applied to the first and second electrodes 202, 204, the shape of the flame 106 can be significantly influenced or controlled.

FIG. 3 is a diagram of a burner system 300, according to an embodiment. The burner 300 is similar to the burner 200 of FIG. 2, and shows an example in which the polarity of the second charge C₂ is the same as that of the first electric charge C₁, resulting in the repulsion of the flame 106 from the second electrode 204, as shown at 106 a. By selection of the polarity and magnitude of the first and second charges C₁, C₂ applied to the flame 106, the position of the flame can be controlled.

It can also be seen in FIG. 3, that the first electrode 202 is positioned so as to be in continuous or frequent contact with the flame 106. It is well known in the art that a flame is electrically conductive. Thus, by making contact with the flame 106 by the first electrode 202, the entire flame can be brought instantly to the same voltage potential as the first electrode. Accordingly, operation of the burner system 300 is not affected by the distance between the first and second electrodes 202, 204, and the degree of influence on the flame by the energy applied becomes a function of the distance between the second electrode and the flame, rather than the sum of the distances between both electrodes and the flame.

According to a preferred embodiment, at least one of the first and second electrodes 202, 204 is separated from the flame 106 by a dielectric gap. This serves to reduce or prevent short circuits between the electrodes, which can consume a significant amount of energy. It is further preferred that if one of the electrodes in to be placed in contact with the flame, it is the first electrode 202 that is in contact, while the second electrode 204 is maintained with a dielectric gap. This enables variability in control of aspects such as flame shape and/or position. Because the strength of an electric field is controlled in part by the magnitude of a voltage difference across a dielectric gap, the position of the flame can be controlled by regulation of the voltage across the gap (or the sum of the gaps). On the other hand, if both electrodes make contact with the flame, the flame will remain in contact, even if the voltage difference is adjusted. Eliminating the ability to modify the flame position.

FIG. 4 is a diagrammatic representation of a burner system 400, according to another embodiment. The system 400 includes a third electrode 402 positioned in the thirds region R₃ opposite the second electrode 204. The voltage supply 406 is configured to apply voltage potentials of opposite polarity to the second and third electrodes 204, 402. As with other embodiments, the second electrode is configured to apply a second charge C₂ to the flame 106, which, in cooperation with a first charge C₁ applied to the flame, can be employed to control aspects of the flame such as shape and position. Additionally, however, the third electrode 402 is configured to apply a third C₃ charge to the flame 106. Because the third charge C₃ is opposite in polarity to the second charge C₂, the effect of the third charge will be opposite that of the second charge. Thus, for example, assuming the first and second charges C₁₃ C₂ each have a positive polarity, the flame will be repulsed by the second electrode 202. Meanwhile, the negatively-charged third electrode 402 will produce a negative field, which will attract the flame 106, thereby increasing the effective control over the flame.

A fourth electrode 404 is also shown in the embodiment of FIG. 4, positioned directly opposite the first electrode 202. Together, the first and fourth electrodes are configured to produce ions to carry a charge to the flame 106. In the embodiment of FIG. 4, the first electrode 202 is configured as an ion-ejecting electrode (generally referred to as a corona electrode), while the fourth electrode 404 is configured as a counter electrode. In operation, a voltage of a first polarity is applied to the first electrode 202 and a voltage of the opposite polarity is applied to the fourth electrode 404. Ions are formed around the sharp tip of the first electrode 202 and are attracted by the opposite polarity charge of the fourth electrode 404. As the ions move toward the fourth electrode 404, they become entrained by the flame 106 and are carried downstream, and thereby introduce a charge to the flame. Turning to FIG. 5, a burner system 500 is shown, according to an embodiment. The system 500 includes a first electrode 502 in the form of a toroid positioned coaxially with the axis A of the nozzle 102 at a transition point between the second region R₂ and the third region R₃. The toroid shape serves to apply a substantially equal field strength around the entire circumference of the flame 106. Additionally, there may be circumstances where it is desirable to position the first and second electrodes 502, 204 as close together as possible, or to distance the first electrode from the nozzle, etc. Under such conditions, the transition between the second and third regions R₂ and R₃ is the furthest point downstream at which an electrode can be positioned where electrical energy can be applied to the flame without directly influencing the position or shape of the flame.

It may be advantageous, in some embodiments, to place both the first and the second electrodes within the third region R₃. Accordingly, in various embodiments the first electrode is positioned above the transition point between the second and third regions R₂ and R₃ while according to others, it is positioned below.

FIG. 6 illustrates an embodiment of a combustion system 600 in which the second electrode 602 has a toroidal shape. As noted with regard to the burner system 500, the toroid shape serves to apply a substantially equal field strength around the entire circumference of the flame 106. Such equal field strength may be desirable in embodiments where the flame height or diameter is to be controlled. For example, application of opposite-polarity charges to the first and second electrodes 202, 602 will tend to cause the flame 106 to shorten while expanding in diameter, as shown at 106 a. Conversely, applying same-polarity charges to the first and second electrodes 202, 602 will tend to cause the flame 106 to become taller while contracting in diameter.

Where the claims us the terms upstream, downstream, these and related terms are to be construed as referring to a position or location of the corresponding element with respect to another element, in relation to a flow that includes a fuel stream, a flame supported by the fuel stream, and combustion products from the flame. Where, for example, a first element is described as being upstream from a second element, the first element is closer, in relation to the flow, to a source of the fuel stream, such as, e.g., a fuel nozzle. In such an arrangement, the second element can also be described s being downstream from the first element.

While various aspects and embodiments have been disclosed, other aspects and embodiments may be contemplated. The various aspects and embodiments disclosed here are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

What is claimed is:
 1. A method for controlling a characteristic of a flame in a burner system, comprising: supporting a flame in a fuel stream; and modifying a characteristic of the flame by: applying a first electric charge to the flame at a first location that is upstream from a buoyancy-dominated flow region of the flame, and applying a second electric charge to the flame at a second location that is downstream from a momentum-dominated flow region of the flame, such that the first and second electric charges interact.
 2. The method of claim 1, comprising identifying a transition point between the momentum-dominated flow region of the flame and the buoyancy-dominated flow region of the flame.
 3. The method of claim 1, comprising identifying the buoyancy-dominated flow region of the flame, and selecting the second location to be within the buoyancy-dominated flow region.
 4. The method of claim 1, comprising identifying the momentum-dominated flow region of the flame, and selecting the first location to be within the momentum-dominated flow region.
 5. The method of claim 1, wherein the applying a first electric charge comprises charging the flame at a first polarity.
 6. The method of claim 5 wherein the applying a second electric charge comprises generating an electric field between an electrode and the flame.
 7. The method of claim 6, wherein the generating an electric field comprises: providing a dielectric gap between the electrode and the flame; and applying a voltage having a second polarity, opposite the first polarity, to the electrode.
 8. The method of claim 5 wherein the charging the flame at a first polarity comprises: applying a voltage potential to an electrode in electrical contact with the flame.
 9. The method of claim 8 wherein: the supporting a flame in a fuel stream comprises ejecting fuel from a nozzle; and the applying a voltage potential to an electrode in electrical contact with the flame comprises applying a voltage potential to the nozzle.
 10. The method of claim 5 wherein the charging the flame at a first polarity comprises introducing ions into the flame.
 11. The method of claim 10 wherein the introducing ions into the flame comprises: generating ions having the first polarity; and entraining the ions into the flame.
 12. The method of claim 10 wherein the introducing ions into the flame comprises: ejecting ions from a corona electrode by applying a first voltage potential having the first polarity to a corona electrode positioned adjacent to the flame while simultaneously applying a second voltage potential having a second polarity, opposite the first polarity, to a counter electrode positioned adjacent to the flame on a side opposite the corona electrode; and entraining the ions into the flame.
 13. The method of claim 1, wherein: the applying a first electric charge comprises applying a first electric charge having a first polarity; and the applying a second electric charge comprises applying a second electric charge having a second polarity, opposite the first polarity.
 14. The method of claim 1 wherein: the applying a first electric charge comprises applying a first electric charge having a first polarity; and the applying a second electric charge comprises applying a first voltage having the first polarity to a first electrode positioned adjacent to the flame while applying a second voltage having a second polarity, opposite the first polarity, to a second electrode positioned adjacent to the flame on a side of the flame substantially opposite the first electrode.
 15. The method of claim 1 wherein: the applying a first electric charge comprises applying a first electric charge having a first polarity; and the applying a second electric charge comprises forming an electric field across the flame at the second location, by applying a first voltage having the first polarity to a first electrode positioned adjacent to the flame while applying a second voltage having a second polarity, opposite the first polarity, to a second electrode positioned adjacent to the flame on a side of the flame substantially opposite the first electrode.
 16. The method of claim 1, wherein the applying a second electric charge comprises: applying a second electric charge having a same polarity as the first electric charge.
 17. The method of claim 1 wherein: the applying a first electric charge comprises applying a first voltage potential to a first electrode positioned adjacent to the flame at the first location; and the applying a second electric charge comprises applying a second voltage potential to a second electrode positioned adjacent to the flame at the second location.
 18. The method of claim 17 wherein: the applying a first voltage potential comprises applying the first voltage potential having a first polarity to the first electrode; and the applying a second voltage potential comprises applying the second voltage potential having a second polarity, opposite the first polarity, to the second electrode.
 19. The method of claim 1 wherein: the applying a first electric charge comprises applying a first voltage potential to a first electrode positioned adjacent to the flame at the first location and having annular shape; and the applying a second electric charge comprises applying a second voltage potential to a second electrode positioned adjacent to the flame at the second location.
 20. The method of claim 1 wherein: the applying a first electric charge comprises applying a first voltage potential to a first electrode positioned adjacent to the flame at the first location; and the applying a second electric charge comprises applying a second voltage potential to a second electrode positioned adjacent to the flame at the second location and having an annular shape.
 21. A method for controlling a characteristic of a flame in a burner system, comprising: supporting a flame in a fuel stream; identifying a flame holding region of the flame, a momentum-dominated flow region of the flame, and a buoyancy-dominated flow region of the flame; modifying a characteristic of the flame by: applying a first electric charge to the flame at a first location that is upstream from the buoyancy-dominated flow region of the flame, and applying a second electric charge to the flame at a second location that is downstream from the momentum-dominated flow region of the flame, such that the first and second electric charges interact.
 22. A method for controlling a characteristic of a flame in a burner system, comprising: in a fuel stream, supporting a flame that is characterized by a momentum-dominated flow region and buoyancy-dominated flow region, each having dimensions sufficient for the application of electrical energy; modifying a characteristic of the flame by: applying a first electric charge to the flame at a first location that is upstream from the buoyancy-dominated flow region of the flame, and applying a second electric charge to the flame at a second location that is downstream from the momentum-dominated flow region of the flame, such that the first and second electric charges interact. 